The present invention relates to a light emitting diode (LED) chip structure, and more particularly to a AlGaInP and a AlGaAs LED structures.
The conventional AlGaInP LED, as shown in FIG. 4, has a double heterostructure (DH), which is consisted of an n-type (AlxGa1xe2x88x92x)0.5In0.5P lower cladding layer 4 with a Al dosage of about 70%xcx9c100%, formed on an n-type GaAs substrate 3, a (AlxGa1xe2x88x92x0.5In0.5P active layer 5, a p-type (AlxGa1xe2x88x92x)0.5In0.5P upper cladding layer 6 with a Al dosage 70%xcx9c100% and a p-type high energy gap GaP or AlGaAs current spreading layer 7. The emitting wavelength of the conventional LED structure can be changed by changing composition of the active layer to generate a wavelength light changed from 650 nm red light to 555 nm pure green light. One disadvantage of the conventional LED is that, when the light generated by the active layer is emitted deep to the GaAs substrate, the light will be absorbed by the GaAs substrate since the GaAs substrate has a lesser energy gap. Accordingly, the performance of the LED will be greatly reduced.
There are some conventional LED technologies have been disclosed in order to avoid the absorption of light by the substrate. However, these conventional technologies still have some disadvantages and limitations. For example, Sugawara et al. disclosed a method, which has been published in Appl. Phys Lett. Vol. 61, 1775-1777 (1992), that adding a distributed bragg reflector (DBR) layer on the GaAs substrate so as to reflect the light ejected to the GaAs substrate and to decrease the light absorbed by the GaAs substrate. However, because the DBR layer only can effectively reflect the light approximated to verticality ejected to the GaAs substrate, so that the efficiency is not very great.
Kish et al. disclosed a wafer-bonded transparent-substrate (TS) (AlxGa1xe2x88x92x)0.5In0.5P/GaP light emitting diode [Appl. Phys Lett. Vol. 64, No. 21, 2839 (1994); Very high-efficiency semiconductor wafer-bonded transparent-substrate (AlxGa1xe2x88x92x)0.5In0.5P/GaP]. This TS AlGaInP LED was fabricated by growing a very thick (about 50 xcexcm) p-type GaP window layer using hydride vapor phase epitaxy (HVPE) together at a temperature above the eutectic point of AuSn solder. After bonding, the n-type GaAs substrate was selectively removed using conventional chemical etching techniques. The exposed n-type layers subsequently wafer-bonded to 8-10 mil thick n-type GaP substrate. The resulting TS AlGaInP LED exhibit a two fold improvement in light output compared to absorbing substrate (AS) AlGaInP LED. However, the fabrication process of TS AlGaInP LED is too complicated. Therefore, it is difficult to manufacture these TS AlGaInP LEDs in high yield and low cost.
Horng et al. reported a mirror-substrate (MS) AlGaInP/metal/SiO2/Si LED fabricated by wafer-fused technology [Appl. Phys Lett. Vol. 75, No. 20, 3054 (1999); AlGaInP light-emitting diodes with mirror substrates fabricated by wafer bonding]. They used the AuBe/Au as the adhesive to bond the Si substrate and LED epilayers. However, the luminous intensity of these MS AlGaInP LEDs is about 90 mcd with 20 mA injection current and is still 40% lower than the luminous intensity of TS AlGaInP LED. Besides, both p-electrode and n-electrode are formed on the same side, so that the chip size can not be decreased. Therefore, the chip size is larger than conventional LED chip that has p-electrode on one side and n-electrode on the other side. Thus, this type of LED chip is difficult to satisfy a case of a package size compatible with the trend toward miniaturization.
As described above, the conventional LED has many disadvantages. Therefore, the present invention provides a LED structure and method of making the same to solve the conventional disadvantages.
The present invention provides a light emitting diode. The light emitting diode comprises a epitaxial structure has a plurality of III-V compound semiconductor layers and can generate light with injection current, a silicon substrate has a first ohmic contact metal layer on one side and a second ohmic contact metal layer on the other side and a low-temperature solder layer for bonding the epitaxial structure and the silicon substrate together.
The present invention provides a method for manufacturing a light emitting diode, which comprises the steps of: providing a epitaxial structure, the epitaxial structure has a plurality of III-V compound semiconductor layers and can generate light with injection current; providing a silicon substrate, the silicon substrate has a first ohmic contact metal layer on one side and a second ohmic contact metal layer on the other side; and, providing a low-temperature solder layer for bonding the epitaxial structure and the silicon substrate together.
An advantage of the present invention is to provide a vertical LED chip structure requiring a single wire bond that results in easy LED assembly and the manufacture cost can be reduced.
An advantage of the present invention is a bonding process can be produced at a lower temperature and a better welding performance can be obtained.
An advantage of the present invention is an LED chip size can be greatly reduced and compatible with the trend toward miniaturization, particularly in surface mount LED applications and saving the material cost.
An advantage of the present invention is with good heat dissipation, therefore the LED has better reliability performance and can be operated at much higher current.
An advantage of the present invention is very easy to mass-produce in high yield and lower cost.